WO 95/25626 has disclosed a method for the production of biaxially oriented plastic tube, also known as a stretched tube. In this method, the stretched tube is of uniform cross section, i.e. has a uniform wall thickness and diameter, over its entire length, and is also uniformly stretched in the axial and tangential (circumferential) direction of the tube over its entire length. A method for providing a tube which has been produced in this way with a socket at one of its ends is known from WO 97/33739.
Another method for producing tube from biaxially oriented plastics material is known from GB 1 589 052. This method is based on a tube made from thermoplastic material which has not been subjected to biaxial orientation, which tube has a tube body with, at one end, an end part with a greater wall thickness than the tube body. The tube is placed in a die and is expanded by an internal pressure so that the plastics material of the tube is biaxially oriented. In the process, the end part is deformed to form a socket.
WO 98/13190 has described yet another method for the production of a tube with an integral socket from biaxially oriented thermoplastic material.
Despite all the developments in the field of the production of tubes from biaxially oriented thermoplastic material, and in particular in the field of forming a socket on a tube of this nature, load tests still show that the socket of a tube of this nature forms the critical part of the tube. This is because the tube has been found to rupture earlier at the socket than in the tube body, and therefore the socket constitutes an undesirable limitation on the mechanical strength of the tube.